An amount of air entering an engine may be estimated via a manifold absolute pressure (MAP) sensor or a mass airflow (MAF) sensor. The MAP sensor has advantages of directly sampling intake manifold pressure to determine cylinder air charge. Consequently, the MAP sensor may provide more accurate engine airflow estimate when the engine intake manifold pressure is changing due to engine load transients. On the other hand, the MAF sensor provides an accurate measure of air mass entering the engine during steady state conditions which may improve engine air-fuel ratio control during steady state conditions. However, output of both the MAP sensor and MAF sensor may be affected by humidity in air since output of each sensor is not compensated for humidity. As a result, engine performance during humid conditions may not be as potent as engine performance during low humidity conditions.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: adjusting spark timing advance/retard responsive to ambient humidity to reduce knock; adjusting engine airflow responsive to desired engine torque, the engine airflow adjusted responsive to a partial pressure of oxygen in air; and adjusting an estimated engine torque responsive to the partial pressure of oxygen in air in addition to the adjusted spark timing retard/advance, the partial pressure of oxygen in air based on ambient humidity.
By adjusting engine spark timing and desired engine airflow responsive to ambient air humidity; it may be possible to provide the technical result of an engine outputting an equivalent amount of torque output during high humidity conditions as the engine outputs during low humidity conditions. Adjusting the desired engine airflow responsive to the partial pressure of oxygen in air may allow the engine to operate with a same amount of oxygen during high ambient air humidity conditions as at low ambient humidity conditions. Consequently, the oxygen flowing through the engine may be matched with a suitable amount of fuel to increase engine torque during high humidity ambient conditions as compared to if the engine airflow is not adjusted for humidity. Further, if the engine control system includes a MAF sensor, the engine airflow may be adjusted responsive to a specific heat of the airflowing through the engine so that the engine operates with a same amount of oxygen during high ambient humidity conditions as at low ambient air humidity conditions. Additionally, spark timing adjustments for humidity may increase spark advance to improve engine torque during humid operating conditions.
The present description may provide several advantages. In particular, the approach may provide more uniform engine performance over a range of ambient air humidity levels. Further, the approach is suited for turbocharged and naturally aspirated engines. Further still, the approach may be applied to mass airflow systems and speed density systems.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.